F4U highest flap speed?

[Noah17]

I didn't want to "hijack" the F6F thread but, I've heard that the F4U could drop flaps up to 300-310MPH. Is that true?

I know F4U flaps and their modeling have been discussed before but don't remember if the top speed for a drop was discussed.

 

[Saxman]

First notch of flaps for the F4U in our game come down at 250mph IAS.

[Noah17]

Yes, in game it's 250. I had heard that the real aircraft could drop higher than that.
I wasn't sure if that was true or not.
Thanks

[texastc316]

Oh if only... We d never hear the end of it.

[BnZs]

Oh if only... We d never hear the end of it.

What difference would it make? The machine is above corner speed at 300 anyway, so the extra lift would account for naught.

[bozon]

Yes, in game it's 250. I had heard that the real aircraft could drop higher than that.

The thing that I always wonder about is how many Gs could the plane pull without damaging the flaps. I am quite sure that the handbook speed limit on deployment assumes G~1, with some tolerance. In the game we lower 30 deg flaps at 250mph and then pull 6G...
The stress on the flap will depend on the lift and induced drag that scale close to linearly with G, and there is an additive term due to parasitic drag. Since lift and induced drag scale like V^2, my guess is that for a given limiting stress on the flap the speed limit will go like V_limit ~ V_book / sqrt(G), at least for G>1. So if the manual says 250mph is the safe limit, then you have to be doing less than 100mph to pull 6G without breaking them (6G at 100mph is of course impossible).

I wish the auto retract (or alternatively, jam flaps) feature would kick in for a speed modified by G load. This way manuevering flaps will be useful only at very low speeds and only the first few notches and we will see a bit less of the flap-fest that flight sims have become.

[SgtPappy]

That is an interesting note, Bozon. The issue of load factors on flaps hasn't really been discussed before huh?

[Bodhi]

The Corsairs have an over speed prevention set up which actually prevents the flaps from coming down (or staying down) at to high a speed.  I have met pilots that have said they dropped their flaps at 350 kts and I believe it.  THe only thing is, that they dropped the flaps in the cockpit only, and the flaps attempt to deploy to be stopped by the over speed prevention.

[SIK1]

Here's what my Pilot's Flight Operating Instructions says.

"flap control shall not be place in position for lowering flaps at speeds in excess 200 knots even though the flaps are protected by an overload release mechanism."

The flaps on a corsair really do "blow up" like in the game. That is the overload release mechanism mentioned.

So no, a real corsair couldn't lower it's flaps at 300 mph at least not a -1, or -1A. (The models my book covers)

[SIK1]

bozon I see no G limitation on use of the flaps only a speed limitation. 

There is this in the Operating Instructions:

"The flaps are also designed for use in maneuvering the airplane in combat. With typical maneuvering flap deflections of 20* or less the airplane may be maneuvered at equivalent limiting "flaps up" accelerations up to 200 knots."

[Noah17]

I remember an account of Ike Kepford being chased by a bunch of Zeke's just above the water. He apparently told Tommy Blackburn that at a high speed he dropped flaps and caused an overshoot of a Zeke. I know that he had been travelling well over 300mph during most of the chase but can't say for sure at that specific time what his speed was.

An interesting side note for me was that apparently his WEP water/methanol mix was used up and his engine was not running that well. Then end result was that he was barely able to out run the Zeke's. Something we do here with ease without WEP in any model F4U.

[bozon]

bozon I see no G limitation on use of the flaps only a speed limitation. 

There is this in the Operating Instructions:

"The flaps are also designed for use in maneuvering the airplane in combat. With typical maneuvering flap deflections of 20* or less the airplane may be maneuvered at equivalent limiting "flaps up" accelerations up to 200 knots."

This is quite a low speed and moderate flap deflection. At these speeds the ability to pull G is very limited anyway. That is exactly my point - flaps as a maneuvering aid are designed to operate at a moderate deflection angle and quite slow speeds. At higher speeds, not only the 1G stress on the mechanism increase, but the ability to overload it by more G also increase. By 250mph, most planes are capable to pulling 6G but at 200mph very few can. I would be very surprised if the flap blow-up mechanism really was controlled by speed and not the actual load on the flap. In that case, the blow-up speed would change with G load.

[SIK1]

iirc the "blow up" mechanism is based purely on speed. The air pushing on the flap literally blows it "back up" that is why at a given speed only a flap setting not exceeding that speed can be achieved even if the flap lever is in the full down position.

Bodhi would know more about this than I do since all my info comes just from books.

Noah I remember the story you are referencing. It comes from Tom Blackburn's book "The Jolly Rogers". I don't recall the dropping flaps at hi speed part but I will look it up and see what it says.

[Bodhi]

Airflow (created by speed) pushes the flap back, preventing damage.  You can still bend the pushrods and attach fittings.  The gear is different in that it unloads when it is delpoyed as a dive brake.  Both have built in overspeed protection.

[bozon]

iirc the "blow up" mechanism is based purely on speed. The air pushing on the flap literally blows it "back up" that is why at a given speed only a flap setting not exceeding that speed can be achieved even if the flap lever is in the full down position.

Airflow (created by speed) pushes the flap back, preventing damage.  You can still bend the pushrods and attach fittings.

The flaps do not read the speed gauge in the cockpit. The force acting on the flap depend on the speed... and on the attitude of the flap relative to the airflow (and the whole wing section near the flap as well). This changes with the angle of attack and for a given speed this means G load. The speeds everyone quote must be for conditions between unloaded and level flight, which are the normal conditions at which flaps are used.